132 Otis F. Curtis 



perature. As has already been stated, this balance can be controlled 

 by the application of heat to the basal part of the cutting while the growth 

 of the tops is retarded by continued low temperature. 



As stated earlier, it has been recognized that in order to form roots 

 a cutting must have available a sufficient amount of elaborated food. 

 In the case of dormant woody cuttings, this food is stored in the twig, 

 while herbaceous cuttings are dependent on such organic matter as is 

 elaborated by the attached leaves. "The practice of ringing the twigs 

 some time before making the cuttings, or ringing or notching before 

 layering, serves merely to increase the supply of this food by checking 

 its removal thru the phloem to other parts of the plant. 



The explanation more commonly given for ringing, is that since this 

 practice tends to increase callus formation it correspondingly increases 

 root formation, because a callus must be formed before the roots will 

 develop. As Corbett (1897) has stated, however, and as the writer has 

 observed, callus formation does not necessarily precede or even accompany 

 root formation. Conditions favoring callus development in cuttings favor 

 root formation also, and conditions that hinder Or inhibit the former proc- 

 ess will usually check the latter. It is true further that if there is insuffi- 

 cient food for vigorous callus production there is a corresponding deficiency 

 for root formation. Vigorous callus development, therefore, is merely 

 an indication that the cutting is in good condition and is well supplied 

 with food, and that the external conditions are favorable for root formation. 

 In the course of the present investigation it has been shown that 

 immature cuttings of Ligustrum and herbaceous cuttings of tomato, if 

 placed in sugar solutions for a limited time, will absorb sugar from such 

 solutions in sufficient quantities to increase root growth. It has been 

 shown also that if such cuttings are left continuously in the sugar solutions, 

 the root formation is largely suppressed. This inhibition is explained 

 as being due, not to the sugar directly, but to the toxic substances formed, 

 as a result of bacterial or fungous action, or to a lessening of the oxygen 

 content coupled with an increase in carbon-dioxide content. As a general 

 rule, propagators are careful to exclude aU easily decomposed organic 

 matter from the medium in which the cuttings are to be grown. The 

 explanation usually given for this practice (Bailey, 1913:54) is that the 

 presence of such organic matter supplies a medium in which fungi can 

 grow, and therefore the plants are more liable to damping-off. From the 



